U.S. patent application Ser. No. 08/911,889, the teachings of which are incorporated herein by reference, is directed to a method of producing aminoanthraquinone blue colorants. The method set forth therein reacts quinizarin and/or its leuco derivative with a mixture of aliphatic amines, wherein the reaction is carried out in the presence of a glycol and/or a glycol ether. Subsequent to the reaction, excess amine and water are removed, leaving a highly concentrated solution of dyes in the glycol or glycol ether. The solution can be directly diluted with a non-polar aromatic solvent to provide a dye solution of high concentration.
While U.S. patent application Ser. No. 08/911,889 described the production of highly concentrated dye solutions, experience has shown that there is a limit to the concentration of such solutions if they are subject to exposure to low temperatures, e.g., -20.degree. C., during shipping and handling.
There has been a need to have even more highly concentrated dye solutions which are stable at low temperatures, i.e., down to -20.degree. C.
The present invention is directed to a dye solution which is the reaction product of quinizarin and/or leuco-quinizarin and a mixture of four particular amines in specific relative molar ratios, which dyes solution can be highly concentrated, yet stable at low temperatures, e.g., down to -20.degree. C.